1. Field of the Invention
The present invention relates to a magnetic record/playback head for digital data, and more particularly to an improved thin film magnetic record/playback head capable of response for bit densities as high as 100,000 flux changes per inch (100 kfci) and at frequencies of 100 megahertz and higher.
2. Description of the Prior Art
Thin film heads fabricated of magnetic core material such as permalloy offer significant improvements in permeability and frequency response, thus allowing higher data transfer rates. These core materials have higher saturation flux densities than do standard ferrites. This factor allows stronger fields to be used during recording and makes feasible the utilization of high coercivity recording media which is required for high linear density recording.
The low input inductance, write-current levels and playback voltages produced by these permalloy thin film designs are well suited to conventional read/write electronics. Therefore, to achieve higher data densities and transfer rates, it is desirable to extend the performance of the magnetic record/playback head without demanding a corresponding advance in electronics technology.
A bit density of 100 kfci means that each "bit" of data has a recorded length of only 10 microinches, or about 0.25 micron, an extremely short distance! To achieve such high density, it is necessary to provide a main gap between the pole pieces of the magnetic record/playback head of less than about 0.25 micron. In order for the head to provide good high frequency response, its pole pieces are made up of very thin layers of magnetically soft material, such as high permeability "permalloy". To suppress eddy currents and other undesirable effects (e.g., domain closures) these magnetic layers, which happen also to be highly conductive electrically, are separated from each other by electrically insulating spacer layers. In prior art devices these spacer layers have typically been made of silica (SiO.sub.2), alumina, or similar highly insulating material, a few hundred Angstroms thick, which is about as thin as can be manufactured in practice without pin holes. It should be noted that each such spacer layer, thin though it is, has a significant thickness compared to a main head gap of only 0.25 micron (250 nanometers or 2500 Angstroms). Each such spacer layer is in effect a secondary magnetic gap in addition to the main gap of the magnetic record/playback head because materials such as SiO.sub.2, while excellent electrical insulators, are also non-magnetic. Where there are a number of these spacer layers, their cumulative thickness may exceed that of the main head gap. This considerably reduces the efficiency of the main gap. As will be explained more fully hereafter, these secondary gaps have undesirably limited the high frequency and high density performance of prior magnetic record/playback heads. This problem is discussed in U.S. Pat. No. 4,799,118 in column 3 thereof.